A crescent PLOT column is disclosed, including a capillary column having an inlet, an outlet, a bore, and an inner surface surrounding the bore and extending between the inlet and the outlet. A layer of particles is localized on a radial portion of the inner surface. The layer of the particles includes a radial thickness decreasing from a center of the radial portion to a periphery of the radial portion, forming a crescent shape in a radial frame of reference. A method for preparing the crescent PLOT column is disclosed, including loading the capillary column with a fluid including a carrier and particles such that the fluid is contained within the capillary column. The capillary column and the fluid contained within the capillary column are subjected to a centrifugal force. The carrier is removed, and a layer of the particles is localized on the radial portion of the inner surface.
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1. A crescent porous layer open tubular (“PLOT”) column, comprising:
a capillary column, the capillary column including:
an inlet;
an outlet;
a bore; and
an inner surface, the inner surface surrounding the bore and extending between the inlet and the outlet; and
a layer of particles localized on a radial portion of the inner surface, the layer of the particles including a radial thickness decreasing from a center of the radial portion to a periphery of the radial portion, forming a crescent shape in a radial frame of reference.
15. A method for preparing a crescent porous layer open tubular (“PLOT”) column, comprising:
loading a capillary column with a fluid such that the fluid is contained within the capillary column, wherein:
the capillary column includes:
an inlet;
an outlet;
a bore; and
an inner surface, the inner surface surrounding the bore and extending between the inlet and the outlet; and
the fluid includes:
a carrier; and
particles;
subjecting the capillary column and the fluid contained within the capillary column to a centrifugal force;
removing the carrier; and
localizing a layer of the particles on a radial portion of the inner surface, the layer of the particles including a radial thickness decreasing from a center of the radial portion to a periphery of the radial portion, forming a crescent shape in a radial frame of reference.
2. The crescent PLOT column of
3. The crescent PLOT column of
4. The crescent PLOT column of
5. The crescent PLOT column of
6. The crescent PLOT column of
7. The crescent PLOT column of
13. The crescent PLOT column of
14. The crescent PLOT column of
17. The method of
18. The method of
19. The method of
20. The method of
loading the capillary column with a second fluid such that the second fluid is contained within the capillary column, the second fluid including:
a second carrier; and
distinct particles;
subjecting the capillary column and the second fluid contained within the capillary column to the centrifugal force;
removing the second carrier; and
localizing a second layer of the distinct particles on the layer of the particles, the distinct particles of the second layer being distinct from the particles with respect to chemical composition, dimension, porosity, shape, coating, or combinations thereof.
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This application claims the benefit of and priority to U.S. Prov. App. No. 62/271,458, filed Dec. 28, 2015, which is hereby incorporated by reference in its entirety.
This application is directed to gas chromatography (“GC”) porous layer open tubular (“PLOT”) columns and methods for forming GC PLOT columns. More specifically, this application is directed to crescent PLOT columns and methods for forming crescent PLOT columns with gravitational deposition.
PLOT columns have been advantageously used for analysis of volatile compounds in gas chromatography. These columns provide high selectivity, which enables optimization of analysis time and increases in laboratory efficiency.
PLOT columns include a column with a thin layer of porous material coating the internal surface of the column. The porous material may be selected based on the materials to be separated, but the retention times for materials in the PLOT columns depend not only on the porous material, but also the column surface on which the porous material is deposited. PLOT columns have been prepared using molecular sieves, alumina, and porous polymers. The PLOT columns may be coated with the porous material using a suspension of the porous material, and then removing the suspension medium to yield a stable uniform layer, or the porous layer may be formed by in-situ polymerization or other chemical reaction.
Generally, the porous material in PLOT columns forms a layer 5-50 μm thick on the inner walls of the column, but these layers tend to be fragile, and the particles of the porous material may dislodge and move during operation. This movement of particles may contaminate detectors, damage valves, increase noise, or even obstruct the column or connectors used. Attempts at improvements in these respects have been disclosed in U.S. Pat. No. 4,793,920 (which discloses a porous plug to catch eluting particles, but which is subject itself to pressure drop-causing blockages), and U.S. Pat. Nos. 5,599,445, 5,607,580, 5,609,756, 5,620,603, and 5,630,937 (which disclose using siloxane polymers to bond the porous material).
Standard commercial techniques for PLOT column production employ coating processes that deposit a full concentric coated inner surface of the column. Scientific literature describing these coating techniques stress the need for a uniform and even thickness layer throughout the column.
Standard commercial techniques employ evaporation-based mechanisms, where vacuum and/or heat is applied and the liquid-gas interface of the solvent propagates down the column as the solvent evaporates. As the solvent front moves further down the column and away from the column opening, the conductance of the volatized solvent decreases and the vacuum in turn decreases. The linear loss of vacuum pressure and the increase in flow resistance results in a practical limit to the length of column that may be prepared as a PLOT column. Standard commercial techniques relying on heat and vacuum also take several hours to achieve for comparatively short lengths of column (30 meters). Deposition procedures relying on localized solvent removal often exhibit irregularly coated surfaces. This is due to the turbulent solvent boiling and off-gassing at the liquid-vapor interface where the PLOT layer is deposited.
There are also practical limits to the inner diameter and length of the column able to be prepared with conventional techniques, because the evaporation-deposition process is dependent on the ability to apply consistent low pressures and evenly remove solvent along the full axial length of the column. As the column length increases, the pressure differential greatly increases from the open end of the column and the site down the column where the evaporation is occurring.
The inner surface of the column may have chemical activity toward select analyte compounds. It is possible to first deactivate, or chemically coat the full inner surface of the column prior to deposition of the crescent. It is also possible to employ a chemical coating that is ‘sticky’ as well as inert. This technique was described in U.S. Pat. No. 9,075,068, in which adhesive traps were localized to the capillary ends or coated over the PLOT layer itself. In the latter case, the chromatographic behavior of the underlying PLOT layer is likely compromised.
With respect to fugitive PLOT particles that are generated during use, the particles may be generated anywhere along the length of the PLOT coated surface, but the prior art solutions all describe particle trap-like devices, where the trap is localized at the column ends. This inherently results in a smaller trap capacity with respect to the PLOT layer within the column, and the requirement the particle trap ends or ‘tails’ be adequately long enough to ensure the capture of all fugitive particles. The presence of unique particle trap ‘tails’ also eliminate the possibility of trimming the columns, which is a common practice in the GC analysis during initial installation and follow-on column maintenance practices. Also when particle traps are connected, the application in vacuum detection systems is problematic as the connections are difficult to create a sufficiently good seal.
Accordingly, it would be desirable to provide PLOT columns and methods for forming PLOT columns not suffering from the above-described drawbacks.
In one exemplary embodiment, a crescent PLOT column includes a capillary column. The capillary column includes an inlet, an outlet, a bore, and an inner surface surrounding the bore and extending between the inlet and the outlet. A layer of particles is localized on a radial portion of the inner surface. The layer of the particles includes a radial thickness decreasing from a center of the radial portion to a periphery of the radial portion, forming a crescent shape in a radial frame of reference.
In another exemplary embodiment, a method for preparing a crescent PLOT column includes loading a capillary column with a fluid such that the fluid is contained within the capillary column. The capillary column includes an inlet, an outlet, a bore, and an inner surface surrounding the bore and extending between the inlet and the outlet. The fluid includes a carrier and particles. The capillary column and the fluid contained within the capillary column are subjected to a centrifugal force. The carrier is removed, and a layer of the particles is localized on a radial portion of the inner surface. The layer of the particles includes a radial thickness decreasing from a center of the radial portion to a periphery of the radial portion, forming a crescent shape in a radial frame of reference.
Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.
Referring to
Referring to
Referring to
Without being bound by theory, it is believed that because the separation mechanism for PLOT-based columns are adsorption driven (rather than dissolution of the analyte into a coated phase), particles 104 in the layer 102 having the crescent shape 314 will interact with an analyte essentially equivalently.
The particles 104 may be porous, non-porous, or a mixture of porous and non-porous particles 104. The particles 104 may include an organic polymer, an inorganic material, combinations thereof, or mixtures thereof. In one embodiment, the particles 104 include a solid substrate and a chromatographic phase disposed on the solid substrate. Particles 104 can be regular and/or irregular in shape and may vary in size from about 1 nm up to about 2000 nm.
The capillary column 108 may include any suitable capillary inner diameter 318, including, but not limited to, a capillary inner diameter 318 of between about 0.1 mm and about 1.0 mm. It will further be appreciated that in some embodiments, microchannel capillary columns may also be employed for PLOT columns. In these cases the bore may be oval, rectangular, or square in shape.
Referring to
Referring to
The interior coating 200 may be formed from any suitable material, including, but not limited to, organosilanes, siloxanes or polyethyleneglycols. In one embodiment, the interior coating 200 is a particle trap. In the crescent PLOT column 300, the interior coating 200 is consistently in close proximity from where a particle 104 may be released during operation of the crescent PLOT column 300, and a considerable portion of the inner surface 106 formed by the interior coating 200 is exposed to the open region 116 of the bore 114. This provides high particle trap coverage of the bore 114, while leaving the layer 102 of particles 104 unencumbered with any overcoat that may compromise the chromatographic performance. Further, because the adhesive trap (interior coating 200) is exposed along the entire axial length 400 of the crescent PLOT column 300, trimming the crescent PLOT column 300 during installation or maintenance is permitted. Further, in an embodiment in which the interior coating 200 includes organosilanes, the organosilane moieties are capable of orthogonal chromatographic separations, forming a parallel configuration for the separation mechanisms of the crescent PLOT column 300, yielding a combination of both PLOT species and phase species.
Referring to
Referring to
The nature of centrifuge application further results in a separation of particles based on their size and density. As a result, a gradient layer may also be created from a particle laden solution containing particles having more than one distinct particle type. Multiple layers of distinct particles may also be applied to form a gradient. The second layer 700 having distinct particles 702 may be localized on the layer 102 of the particles 104 which is disposed on the capillary material 110 (shown) or on the layer 102 of the particles 104 which is disposed on an interior coating 200 (not shown for this specific embodiment, but analogous to
Referring to
Referring to
Containing the fluid 900 within the capillary column 108 may include plugging the inlet 302 and the outlet 304 following introduction of the fluid 900.
In one embodiment, the radial thickness 308 increases or decreases with the increase or decrease, respectively, of the concentration of the particles 104 in the fluid 900. The precise crescent shape 314 formed may be influenced by a combination of the concentration of the particles 104 in the fluid 900, the cross-sectional shape of the bore 114, and the topological shape of the inner surface 106.
The centrifugal force may be uniform or non-uniform. Subjecting the capillary column 108 to the centrifugal force may include spinning the capillary column 108 and the fluid 900 contained within the capillary column 108 about the central axis 800. Spinning the capillary column 108 and the fluid 900 contained within the capillary column 108 may be performed with a centrifuge (not shown).
In one embodiment, subjecting the capillary column 108 and the fluid 900 contained within the capillary column 108 to the centrifugal force localizes the layer 102 of the particles 104 essentially uniformly, alternatively uniformly, along an axial length 400 of the inner surface 106.
Preparing the crescent PLOT column 300 may occur over any suitable length of time commencing with loading the capillary column 108 with the fluid 900. In one embodiment, preparing the crescent PLOT column 300 commencing with loading the capillary column 108 with the fluid 900 occurs in less than about two hours, alternatively less than about one hour, alternatively less than about 45 minutes, alternatively less than about 30 minutes. The rotational speed (number of revolutions per minute) and spin duration conditions are primarily dependent on the cross sectional area of the column, column coil radius, particle composition and morphology, and solvent viscosity.
Referring to
A comparative example (with no particles 104) and an inventive example (analogous to
Deactivation of the inner surfaces 106 of the comparative example and the inventive example was achieved by preparing a deactivation solution by dissolving polyethylene glycol (PEG; H—(O—CH2—CH2)n—OH average MW 20,000) in dichloromethane (CH2Cl2), and then wetting the inner surfaces 106 by passing one volume of the deactivation solution completely through the capillary columns 108. The capillary columns 108 were then dried under an inert gas flow, heated under an inert gas flow, rinsed with CH2Cl2, and then dried again under an inert gas flow.
Preparation of the inventive example included preparing the fluid 900 by adding a powdered porous polymer (composition being a copolymer of ethylene glycol dimethacrylate and divinylbenzene) (the particles 104) to a carrier 902 comprising a solvent mixture of CH2Cl2and pentane, the concentration of the particles 104 in the fluid 900 being about 2.3% wt/vol). The fluid 900 was mechanically shaken until homogeneous. The fluid 900 was placed into a pressurized vessel with one end of the capillary column 108 inserted into the vessel below the liquid meniscus of the fluid 900. Nitrogen pressure was then applied to the vessel, forcing the fluid 900 into the capillary column 108. After the capillary column 108 was filled with the fluid 900, the pressure in the vessel was released and one end of the capillary column 108 was sealed.
The capillary column 108 was coiled (to about a seven inch coil diameter 802) inside of a custom-fabricated rotor adapter and placed horizontally inside of a HERAEUS INSTRUMENTS LABOFUGE 400 centrifuge, and centrifuged at a rate of about 3500 rpm for 60 minutes. The capillary column 108 was then carefully removed from the rotor adapter so as to avoid disturbing the stratification of the particles 104 along the inner surface 106. The capillary column 108 was then suspended horizontally in a 30° C. water bath (allowing full water circulation around the capillary column 108), with the sealed end secured above the water level in the bath and the other (free) end of the capillary column 108 connected to a closed vacuum port on a manifold connected to a vacuum pump capable of generating a vacuum of 40 Torr (about 1.5 inches of Hg). The vacuum port was switched to the on position to begin evaporating the carrier 902 inside the column. The evaporation proceeded to completion over 18 hours, leaving behind the layer 102 of the particles 104 having the crescent shape 314, and thereby forming a crescent PLOT column 300. The crescent PLOT column 300 was disconnected from the vacuum port and removed from the bath. The sealed end of the crescent PLOT column 300 was clipped off, and the crescent PLOT column 300 was heated under an inert gas flow (15 psi head pressure) to 190° C. for 18 hours.
Each of the comparative example and the inventive example were installed into a GC having the following attributes and settings:
Each of the comparative example and the inventive example were injected with 1.0 μL of “Q-BOND and U-BOND Column Test Mix” (Restek catalog. #:35202):
The test mix solvent (heptane) eluted after all the analytes of interest. Data collection was halted after the elution of the final analyte (ethyl acetate). The chromatographic run continued to ensure the elution of the solvent (heptane) from the column.
Referring to
Referring to
While the foregoing specification illustrates and describes exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Kane, Thomas E., De Zeeuw, Jaap, Bromps, William P., Peters, Tracey
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